Field of the Invention
The present invention relates to compounds of the general formula I ##STR2## where R is hydroxyl or unsubstituted or substituted amino, R.sup.1 is hydrogen or C.sub.1 -C.sub.12 -alkyl, X.sup.1 and Y.sup.1 independently of one another are each a carboxylic acid ester or ether group and X.sup.2 and Y.sup.2 independently of one another are each hydrogen, nitro or chlorine.